120 patients scheduled to undergo lower extremity surgery were included in one of three groups. Determination of median effective (ED50) doses was performed by the Dixon and Mood up-and-down method. Initial doses was 1μg/kg, with dose adjustment intervals of 0.05μg/kg, in the youth,and middle-aged group. The initial doses of DEX was 0.7 μg/kg,also with dose adjustment intervals of 0.05μg/kg.Sedative efficacy was defined as an OAA/S of ≤2, or an OAA/S of 3 but with an BIS value of ≤46, 26 min after the beginning of drug administration.